1. Technical Background
The present invention relates to a medical filter which can be placed inside a blood vessel or other body passage for the purpose of intercepting thrombus or particles, which may be optionally retrieved at a later time.
2. Discussion
Some basic types of medical filters are generally known, wherein a single filter element, mesh or member extends across the direction of flow inside a blood vessel. Several features are desirable for medical filters, including non-surgical or percutaneous delivery of the filter to a desired site, and expansion from a preferably small initial size to an expanded working size that matches the vascular anatomy at the desired site. Also, a medical filter should of course preferably capture a sufficient percentage of thrombus, while allowing blood to flow freely through the filter.
Another desirable feature is a capability to remain in the desired position for treatment through a period of time, and also to offer the physician the option during that time of leaving the filter in place permanently, or retrieving the filter when no longer needed.
In addition, a medical filter should preferably have a design whereby the filter is stable in the vessel, such that the filter has little or no tendency to “tilt” and may become less effective in capturing thrombus. Some medical filters may be used in the vena cava, and may be described in such event as a “vena cava filter.”
Prior medical filters may consist of a network of interconnected ribs, which extend substantially in a radial direction in relation to the blood vessel. Unfortunately, an entire filter may shift position if one of the ribs were to break. In addition, the free ends of the ribs, which may be positioned under a certain pressure against the internal wall of the blood vessel, may cause trauma to the vessel wall, or may become embedded within.
Another possible design is essentially a screen placed across a transverse dimension of a vessel. Again, it is important to take measures to resist “tilting” by this screen type of filter.
A disadvantage of some known medical filters may be a possibility of shifting position or tilting inside the blood vessel, even when the filter maintains its proper shape, if a prior filter may have been incorrectly placed in a blood vessel which is too wide. In such an event, a medical filter may not grab sufficient hold on the internal wall of the blood vessel.
A medical filter may be delivered through a catheter in a compressed shape, where it tends to resiliently expand within the blood vessel. The medical filter may tend to trap thrombus or particles, and resist their movement further downstream. The filter may include, in a position of use, an outer shape corresponding to the internal diameter of the blood vessel transverse to the longitudinal direction hereof.
A medical filter which may also be implanted permanently or temporarily. It is preferable to implant the filter initially without deciding at that time whether the filter will eventually be retrieved or is to remain permanently. It is also desirable that if the filter is retrieved, then it should be retrieved as easily as possible.
To help in successful retrieval, a desirable factor is to avoid endothelialization or in-growth of the vessel wall around the structural members of the filter.
On a retrievable filter, it is also desirable to provide releasable temporary position stabilizers, to resist a possibility of tilting and to enhance position retention.
Some medical filters provide anchors or small barbs, which extend at various angles in radial directions outward from the ribs. One successful design which is sufficient for a variety of applications is shown in the commonly owned U.S. Pat. No. 6,443,972, entitled “Vascular Filter” which issued to at least one of the co-inventors of the present invention on Sep. 3, 2002. This patent shows many desirable features for filters, including a longitudinally stable central body section, and two filter sections providing multiple filtering action. Other advantageous features are that it is preferably made of a single piece of resilient material, and can be implanted through a catheter without requiring surgery.
A filter may be provided with barbs or anchors for increasing position retention. The barbs tend to gently hold the filter in place inside the blood vessel, and so it is of course desirable to avoid endothelialization of the filter components, to facilitate its retrieval.
Also, medical filters of the present invention that are retrievable, rather than permanent filters, may provide an additional advantage. When a medical filter is retrieved from a blood vessel, the entire filter is resiliently compressed to a relatively small diameter, for extraction through a catheter.
The filter may preferably have a hook structure at one or both ends, of a design that preferably provides multiple hook surfaces for increasing ease of retrieval.
A filter according to the present invention may also preferably have one or more small barbs or anchors. An additional design is to provide a filter with a hook structure at one end, and cooperating barbs for holding the filter in position, that are arranged to pull out gently if the filter is retrieved in a retrieval direction by pulling on the hook structure with a retrieval snare or other retrieval device.
With a medical filter according to the present invention, a tubular section may tend to resiliently exert slight pressure along a large section of contact area on the wall of the blood vessel or other body passage, which tends to hold itself in place. The medical filter will consequently tend not to shift position.
The term “tubular” is used in its broadest sense, to encompass any structure arranged at a radial distance around a longitudinal axis. Accordingly, tubular includes any structure that (i) is cylindrical or not, such as for example an elliptical or polygonal cross-section, or any other regular or irregular cross-section; (ii) has a different or changing cross-section along its length; (iii) is arranged around a straight, curving, bent or discontinuous longitudinal axis; (iv) has an imperforate surface, or a periodic or other perforate, irregular or gapped surface or cross-section; (v) is spaced uniformly or irregularly, including being spaced varying radial distances from the longitudinal axis; (vi) has any desired combination of length or cross-sectional size.
In addition, the medical filter according to the present invention tends not to rotate transversely or tilt over, which is another advantage of the present invention. In a possible embodiment, a medical filter according to the present invention may preferably be formed out of one single piece, which provides advantages including simplicity of manufacture.
In a preferred embodiment, a medical filter according to the present invention includes a first and second filter section, arranged on either side of a central body section. The body section and the filter sections thus enclose a space. Due to the elongated shape of the medical filter according to the present invention, and the arranging of the first and second section on either side of the body member, the present filter has an enhanced filtering effect. In other words, two filtering structures have been created for intercepting thrombus, particulates or other matter moving inside the blood vessel or other body passage.
Another possible embodiment of the filter according to the present invention is that, when seen in an axial or longitudinal direction, the filter sections have the shape of a regular polygon, and provide several smaller filtering “cells.” The purpose of these filtering cells is to intercept thrombus moving inside a blood vessel, and the smaller filtering cells tend to capture more thrombus.
The filter sections, as arranged according to an embodiment described above on either side of the tubular body section, may be identical in shape, thereby enhancing the simplicity of the medical filter according to the present invention.
Another possible benefit of the present invention relates to endothelialization, which is the healing of the vessel inner surface by endothelial cells. It is desirable not to damage these endothelial cells when removing a retrievable medical filter, and the improved designs of the present invention tend to minimize any impact during retrieval.
Some medical filters may have been made of a braiding of wire-like elements, or a tubular element also having a series of cuts at places corresponding to the positions of passages. It is thus possible to build various medical filters according to the present invention, by various techniques and of various materials to obtain the ultimate shape and desired design. Possible junctions of filter components may be formed by melting or welding free ends together, or by employing such a cutting pattern that the basic shape of the medical filter according to the present invention is obtained.
It should be noted that the present invention also relates to methods for using implantable filters as described herein.
These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings. The invention will be explained in greater detail below with reference to the attached drawings of a number of examples of embodiments of the present invention.